1. Field of the Invention
The present invention relates to a non-exposure process, and more particularly, to a UV curable liquid pre-polymer to improve a thermal stability by changing ingredients of an overcoat layer or by changing ingredients of a column spacer in addition to the overcoat layer. The present invention also relates to a liquid crystal display (LCD) device using the UV curable liquid pre-polymer and a method of manufacturing the LCD device.
2. Discussion of the Related Art
A minute pattern process used in an electric circuit is an important factor that affects the device properties and capacity. Non-exposure processes have become more important in recent years.
One non-exposure process, namely, In-Plane Printing, uses a UV curable liquid pre-polymer as a pattern material. However, the UV curable liquid pre-polymer is weak once heat-treated, where the UV curable liquid pre-polymer shrinks or contracts. When using an In-Plane Printing process using a soft mold to form an overcoat layer and a column spacer as one body, or to form a white color filter layer with an overcoat layer and the column spacer together in a white plus structure, the column spacer, the overcoat layer or the white color filter layer may shrink due to the heat treatment. This may occur, for example, during the baking process after forming an alignment layer on the column spacer.
A related art UV curable liquid pre-polymer and a method of manufacturing an LCD device will be described with reference to the accompanying drawings. FIG. 1 shows a pictorial drawing of a quad-type single pixel including a white sub-pixel. An LCD device patterned by a UV curable liquid pre-polymer includes first and second substrates facing each other and a liquid crystal layer formed between the first and second substrates. Each of the first and second substrates includes a plurality of pixel regions, wherein each pixel includes red (R), green (G), blue (B) and white (W) sub-pixels, as shown in FIG. 1. Also, red (R), green (G), blue (B) and white (W) color filter layers 12a, 12b, 12c and 14 are respectively formed in the red (R), green (G), blue (B) and white (W) sub-pixels.
This structure having the white (W) sub-pixel in addition to the red (R), green (G) and blue (B) sub-pixels is referred to as a “white plus structure.” In FIG. 1, a quad-type one pixel is divided into four portions, wherein the red (R), green (G), blue (B) and white (W) sub-pixels are respectively positioned in the four portions of the quad-type single pixel, which shows the white plus structure. The red (R), green (G), blue (B) and white (W) sub-pixels may be arranged in the shape of a stripe, and the corresponding color filter layers may be respectively formed in the sub-pixels.
FIGS. 2A to 2C show cross sectional views illustrating a method of manufacturing a color filter array substrate in a quad-type pixel structure. FIG. 3 shows a cross sectional view of illustrating shrinkage or contraction in a color filter array after baking the alignment layer.
Referring to FIG. 2A, a light-shielding layer 11 is formed in the boundaries of sub-pixels on a first substrate 10 defined by a plurality of pixels, where each pixel includes red (R), green (G), blue (B) and white (W) sub-pixels. The light-shielding layer 11 is formed in the boundaries of sub-pixels on the first substrate 10, which corresponds to a gate line, a data line and a thin film transistor formed on a second substrate (not shown). A red color filter layer 12a, a green color filter layer (see FIG. 1, 12b) and a blue color filter layer (see FIG. 1, 12c) are respectively formed in the red (R), green (G) and blue (B) sub-pixels of first substrate 10.
A pattern material layer 13 of UV curable liquid pre-polymer is then coated on an entire surface of first substrate 10, including the light-shielding layer 11 and the red (R), green (G) and blue (B) color filter layers 12a, 12b and 12c. The pattern material layer 13 of UV curable liquid pre-polymer is cured by UV light, which pre-polymer is more viscous than a general polymer, and is changed by pressure.
As shown in FIG. 2B, a mold 20 having a backplane (not shown) formed on the rear surface thereof is brought into contact with the pattern material layer 13 to form a pattern 130 in the pattern material layer 13 corresponding to concave and convex portions of the mold 20. Referring to FIG. 2C, the mold 20 is separated from the pattern 130. As a result, the pattern 130 is formed of a white color filter layer 14 provided in the white sub-pixel, an overcoat layer 15 provided on the entire surface of first substrate 10 (including the light-shielding layer 11 and the red, green, blue and white color filter layers 12a, 12b and 12c), and a column spacer 16 provided on the overcoat layer 15 above the light-shielding layer 11. After completing the above-mentioned steps, the white color filter layer 14, the overcoat layer 15 and the column spacer 16 are integrally formed as one body and constitute the pattern 130.
FIGS. 2A to 2C show the white sub pixel and its layers, wherein the white color filter layer is formed during the process of forming the overcoat layer and the column spacer rather than forming the white color filter layer as an additional color filter process step. With respect to the column spacer 16, the overcoat layer 15 and the white color filter layer 14 are patterned together by one pattern material layer. When forming an alignment layer 18 of polyimide on the surface of pattern 130, the alignment layer is baked by a heat treatment of about 180 degrees Centigrade. In this case, the overcoat layer becomes uneven due to the shrinkage or contraction of UV curable liquid pre-polymer. It is necessary for the white sub pixel to properly maintain both the thickness 14a of white color filter layer and the thickness of overcoat layer 15a. Thus, the pattern surface 130a of white sub pixel is more recessed or shrunken than the other portions by the contraction or shrinkage of UV curable liquid pre-polymer during the process of baking the alignment layer 18.